Understanding the Relationship Between Hashing Algorithms in X.509 Certificates and Communication
The two are unrelated. It’s possible for the hash function used for the certificate signature to be different from the hash function used for data integrity during the TLS handshake. However, SHA256 is often used for both nowadays, as earlier hash functions (e.g. SHA1, MD5, etc.) are thought to have weaknesses, and SHA256 is now widely supported for both uses cases.